The present invention relates to a transmission screen used for example in a projection television set and a slide projector. The invention also relates to a method of making such a transmission screen.
A conventional transmission screen disclosed in for example Japanese Patent Kokai Publication No. H3-220542 is shown in FIG. 5. As illustrated, it comprises a semitransparent lenticular lens anti a transparent Fresnel lens 2 on the rear side of the lenticular lens 1. The lenticular lens 1 is the formed of a screen material such as acrylic resin in which light scattering material such as glass powder is mixed. The Fresnel lens 2 is formed of acrylic resin or the like. Provided on the front and rear sides of the lenticular lens 1 are arrays of semi-cylindrical lenses forming lenticular surfaces 1a and 1b. Provided in front of the lenticular lens 1 are black stripes 3 made up of a light absorbing material and formed by printing, to cover the areas other than the areas through which light is to be transmitted. The black stripes 3 are provided to absorb light incident from the outside, e.g., room illuminating light. If the black stripes 3 were not provided, the external light incident on the lenticular lens 1 would be scattered by the light scattering material in the lenticular lens 1. This would increase the brightness throughout the screen, and the contrast of the image as seen from the front side (the right side in FIG. 5) would be lowered. A transparent coating (thin film) 4 of a fluorine resin compound is formed on the front surface of the lenticular lens 1 and the rear surface of the Fresnel lens 2. The transparent coating has a low refraction index, and lowers the reflection of projection light and external light incident on the lenticular lens 1 and the Fresnel lens 2 which are formed of an acrylic resin as a basic component. In this way, the transparent coating 4 increases the contrast of the image on the screen.
The light absorbing layer in the form of black stripes are formed by printing. Such printing is conducted after the molding of the lenses. Thus, complicated steps are involved in such printing. Moreover, visual alignment (alignment by observation with human eyes) is difficult.
It was proposed, as disclosed in Japanese Patent Kokai Publication No. S58-57121, to provide an ink application roller having a number of larger diameter portions (annular projections) juxtaposed with each other and provided at positions confronting the projecting parts of the lenticular die. An ink is coated or applied, by means of a roller, to the peripheral surfaces of the larger diameter portions of the application roller. The ink contains a light absorbing material, and also contains as the binder which can be thermally laminated with the screen material. When the lenticular lens is molded, the ink on the peripheral surfaces of the larger diameter portions is thermally laminated with the front surface of the non-transmissive parts of the lenticular lens, between the lenticular die roller and the ink application roller.
Providing transparent coatings having a low refraction index, on the front and rear surfaces of the lenticular lens or the Fresnel lens, as described in connection with the prior art example of FIG. 5, is effective for increasing the contrast of the image. However, when a transparent coating is formed over the entire lens surface, a large amount of the material is required, and a long time is needed for forming the coating. Thus, it imposes limitations to the productivity and the cost. A method for forming the transparent coating in a short time is to use the ink application roller having juxtaposed larger diameter portions as disclosed in the above-mentioned Japanese Patent Kokai Publication No. S58-57121. This method is effective when the stripes are formed on a flat surface, but is not applicable to a situation where a coating is to be formed over the entire lenticular surface.